Cicadas, whose wings inspired anti-reflective coatings on solar panels and windows, could now help usher in a new era of self-cleaning construction materials, according to new research.
James Cook University
The scientists say that drops of water merge and then jump off the flying insect’s wings.
A team of scientists from Duke University (Durham, NC) and James Cook University (Queensland, Australia) say they have discovered how the red-eyed insects keep their wings clean and free from contaminants.
The secret? Self-propelling dew drops.
The scientists published their research in the journal Proceedings of the National Academy of Sciences in April.
Different from ‘Lotus Effect’
“Traditionally, cleaning of natural surfaces was thought to take place primarily by the so-called ‘lotus effect,’” co-author Dr. Jolanta Watson, of James Cook University, said in an announcement on the research.
In that effect, first observed on the lotus leaf, “rain water droplets roll along the leaf and carry away dirt from the surface, much like water droplets on [the] hood of a freshly waxed car,” she said.
However, the team—led by Chuan-Hua Chen, of Duke’s Pratt School of Engineering—says Mother Nature uses other ways to clean surfaces, especially in areas where rain does not fall for extended periods of time.
The findings are “fundamentally different from the conventional wisdom involving rolling or colliding droplets on a superhydrophic surfaces,” according to Chen.
Merging and Jumping Dew
When cicada’s wings are exposed to water vapor, dew forms small droplets that merge together spontaneously and are self-propelled off the surface by changes in the surface energy, according to the scientists.
The jumping is automatic, and droplets can rid the superhydrophic surface of dirt and other contaminants.
The insects' wings are characterized by rows and rows of small bumps or domes of various heights and widths, Duke University said in its report on the research.
“Most cicadas are unable to clean their own wings because of their short appendages,” said co-author Dr. Gregory Watson of James Cook University. “Furthermore, these insects commonly live in areas where there is little rain over an extended period of time.
"However, the areas are humid, which provides the tiny dew droplets needed to ‘jump clean’ their wings.”
The team dubbed the cleaning effect the “Cicada Effect” as the cicada wing was the first natural surface to illustrate the phenomenon, the scientists noted. This video shows the jumping dew drops.
Variety of Applications
The new discovery may lead to a wide range of applications, according to co-author Dr. Greg Watson.
“The findings gives us a blueprint to copy and make the next new generation of man-made self-cleaning surfaces that can clean themselves of dirt, bacteria and other environmental contaminants,” he said in a statement.
“These types of surfaces may find applications as self-cleaning windows, hospital surfaces, environmentally green surfaces, construction materials, pipes, kitchen surfaces, roof tiles, machine components and water-resistant surfaces.”
Colleagues are impressed with the team's findings.
“This is a great piece of work that highlights a mechanism that has not been conventionally considered for self-cleaning,” Evelyn Wang, a mechanical engineer at the Massachusetts Institute of Technology, said in a report on insidescience.org.
New Research Area
The team also says the findings may prompt a new area in scientific research.
Properties of the spontaneously jumping droplets could be investigated as they could carry specific chemical particles/packages and deposit them onto a variety of surfaces for development in micro-biosensors and nano-delivery systems, the team adds.
The research is supported by the National Science Foundation, the Defense Advanced Research Projects Agency and the North Carolina Space Grant.
Other members of the research team were Duke’s Xiapeng Qu and Fangjie Liu, as well as Katrina Wisdom, a Pratt undergraduate research fellow. Wisdom is listed at the first author of the study.